CA2014367A1 - Process for forming diamond coating using a silent discharge plasma jet process - Google Patents
Process for forming diamond coating using a silent discharge plasma jet processInfo
- Publication number
- CA2014367A1 CA2014367A1 CA002014367A CA2014367A CA2014367A1 CA 2014367 A1 CA2014367 A1 CA 2014367A1 CA 002014367 A CA002014367 A CA 002014367A CA 2014367 A CA2014367 A CA 2014367A CA 2014367 A1 CA2014367 A1 CA 2014367A1
- Authority
- CA
- Canada
- Prior art keywords
- forming diamond
- diamond coatings
- gas stream
- further characterized
- plasma
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
- C23C16/27—Diamond only
- C23C16/276—Diamond only using plasma jets
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
- C23C16/27—Diamond only
- C23C16/277—Diamond only using other elements in the gas phase besides carbon and hydrogen; using other elements besides carbon, hydrogen and oxygen in case of use of combustion torches; using other elements besides carbon, hydrogen and inert gas in case of use of plasma jets
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/50—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges
- C23C16/513—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges using plasma jets
Abstract
Patent 0958p Calcote Case 1 PROCESS FOR FORMING DIAMOND COATINGS
USING A SILENT DISCHARGE PLASMA JET PROCESS
ABSTRACT OF THE DISCLOSURE
A process for forming diamond coatings is disclosed, in which a gas of a mixture of gases is passed through a low temperature silent discharge to generate a low temperature non-equilibrium plasma gas stream, the plasma gas stream is adiabatically expanded into a region of lower pressure to form a plasma gas stream of highly ionized and dissociated gases, a carbon-containing gas is injected into the plasma gas stream during of after the expansion into a region of lower pressure, and the plasma gas stream is then directed onto the surface of a substrate to form the diamond coating.
USING A SILENT DISCHARGE PLASMA JET PROCESS
ABSTRACT OF THE DISCLOSURE
A process for forming diamond coatings is disclosed, in which a gas of a mixture of gases is passed through a low temperature silent discharge to generate a low temperature non-equilibrium plasma gas stream, the plasma gas stream is adiabatically expanded into a region of lower pressure to form a plasma gas stream of highly ionized and dissociated gases, a carbon-containing gas is injected into the plasma gas stream during of after the expansion into a region of lower pressure, and the plasma gas stream is then directed onto the surface of a substrate to form the diamond coating.
Description
095~p 2~3~
Thi~ invention relates to processe~ for preparing diamond coatings.
The mechanical, therEal, electrical and optical ~ro-pertie~ o~ diamond ~ilms offer ~ajor advantages i~ a number oP areaQ includin~ providing e~tremely hard ~ur~aces, impro~-in~ ~e~iconductor~ that ca~ benefit ~ro~ their high th~rmal conductivity and electrical in~ulating properties, and window application~ that benefit ~rom their transparency to photon~.
Th~ preparation o~ dia~o~d coating~ usin~ plas~a chemi-cal vapor teposition (CVD) i~ w~ll g~ow~. Plas~a CV~
involves ror~i~g a plas~a contai~i~g activat2d fres radi-cals, ato~, ions, and electron~ (often called "activated 3pecies"), by u~ing a direct currlent (dc), low frequency, radio ~requency (RF), or microwav~e discharge and then contacting a substrate with tho h.ighly ionized and dls-~ociatet pla~ma ~as to ~or~ a di~no~d coatin~.
Th~ electrical di~charges u~led to ~or~ such pla~ma~
such a~ glow, corona, ratio Pr~qul~cy, ~icrowave, electrode 20 le88, and th~ so-call~d ozoaiz~r di~ch~r~ o~ the one hand, and arc discharg~s on th~ other ha~d, ca~ ge~rally be divid~d r~s~c~v~ly i~to low te~peratur~ proce~e~ and hi~h ~e~perature p~oce~es.
Thi~ invention relates to processe~ for preparing diamond coatings.
The mechanical, therEal, electrical and optical ~ro-pertie~ o~ diamond ~ilms offer ~ajor advantages i~ a number oP areaQ includin~ providing e~tremely hard ~ur~aces, impro~-in~ ~e~iconductor~ that ca~ benefit ~ro~ their high th~rmal conductivity and electrical in~ulating properties, and window application~ that benefit ~rom their transparency to photon~.
Th~ preparation o~ dia~o~d coating~ usin~ plas~a chemi-cal vapor teposition (CVD) i~ w~ll g~ow~. Plas~a CV~
involves ror~i~g a plas~a contai~i~g activat2d fres radi-cals, ato~, ions, and electron~ (often called "activated 3pecies"), by u~ing a direct currlent (dc), low frequency, radio ~requency (RF), or microwav~e discharge and then contacting a substrate with tho h.ighly ionized and dls-~ociatet pla~ma ~as to ~or~ a di~no~d coatin~.
Th~ electrical di~charges u~led to ~or~ such pla~ma~
such a~ glow, corona, ratio Pr~qul~cy, ~icrowave, electrode 20 le88, and th~ so-call~d ozoaiz~r di~ch~r~ o~ the one hand, and arc discharg~s on th~ other ha~d, ca~ ge~rally be divid~d r~s~c~v~ly i~to low te~peratur~ proce~e~ and hi~h ~e~perature p~oce~es.
-2- 2~ 3~
In high temperature di~charge , such as electrical arc~, the concentration of activated ~pecies require~ a thermodyna~ic equilibrium favoring the activated product.
In ord~r to produce a significant amount of acti~ted ~pecie~, e~tremely high temperatures, e.g. temperatures o~
at lea~t 4000R are required. Temperatures as high aQ
10,000 to 30,000K may be u~ed, which mean~ that most of the heat is u3ed to heat the ga~, a great amount of power iQ
required, and the ~ub trate i8 heated to the e~tent that graphi~e and a~orphous carbon may b~ ~ormed instead of dia-~ond, and e~en to the e~tent that the substrate may b~
destroyed, unless the ~ub~trate i8 cooled. Problem~ a8~0-ciated with the th~rmal stability o~ the substrate and di~ference~ between the coef~icient~ of expan~ion o~ the ~ubatrate and the depo~ited diamond film li~i~ the types o~
sub3trate~ that can be used.
For in~tance, in a high tem~eratur~ ~yate~ de~cribed in ~urihara et al., A~ bY~. Le~ 2(6) 19:pp 437 and 438 (1988) and in ~uropean Patent App~ication 0286306 a thermal plasma i8 ~or~ed by passing a mi~:ur~ og methane and hydro-gen through an arc discharge and i~jecting methane into ~he area o~ th~ arc or below it. Tho plas~a i8 pa~ed through a nozzle, espanded to precipitate da~ond and ~inally directed onto a 8ub~trat~ rihara e~ al. 8u~e8t that the problem of ~o~ 8 graphite or amorphous carbon on the substrate becau~ o~ th~ h~gh te~peratures ca~ b~ o~erco~e by w~ter-coolln~ the ~ubstrate.
~ thod~ ~or pr~paring diamond ellm~ that do not require a ther~odyn~ic equilibrium ~àvoring the aetivated produc~, that 13t by ge~ra~in~ a low tem~erature no~-equilibri~
plasm~ for ch~ical vapor depo~ition, have been de~cribed.
Low temperature discharges, include glow di~charges, corona~, electrodeles~ di~charges, and ozonizer di~charge~, as well a~ ~o~ RF and ~icrowave di~charges9 are ganerically ~nown 2~3~7 as a8 "~ilent discharges". Chemical activation in low temperature 8y8te~8 results in a non-equilibrium produc~ o~
the activated species. The concentration of ions and free radical~ in such plasma~ i~ much greater than would be expected on the basis o~ ~h~rmal equilibrium con~iderations.
The use o~ a non-equilibrium plasma jet in a di~ferent conte~t i8 describ~d in a report entitled ~Synth@~is of Silane and Silicon in a Non-equilibrium Plasma J@t", authored by H. F. Caleote (~.S. Department o~ Energy/Jet Propulsion Laboratory Report 954560-76/8), which di3clos~
~orming the plasma by a DC discharge, sub~equently expanding it through a nozzle to form a plasma jet, and directing the jet upon a substrate to prepare adh~rent 8ilicon films.
The u~e of a low temperature plas~a produced by passing a mixture o~ plasma-producing gasses, incluting a carbon-con-taining ~a~, through a glow di~charge to ~orm diamond coat-ings i~ ~u~ested in ~.S. P~tent No. 4,767,~08, but the pro-cess it di~close~ as being useful actually forms a high tem-perature plasma CVD by using an electric arc discharge to decompo~e a carbon 80urce and g~nerate a plasDa gas contain-ing carbo~ ions or carbon radicals. The plasma g~8 i8 ~ubse-quently adi~batically espanded the to precipitate diamond on a 8ubatrate. Since t~s patent al80 Btate~ that the proces~
U8~g a low temp~rature plasma results ~n a very 810~ rate o~ dia~ond ggowt~, it strongly ~ug~est~ that an~ one o~ the low te~pera~ur~ proce~ses i~ ~ot ~fective.
Th~ i8 a need for a di~Xere~t approach to Porming dia-`mond coati~gs, name~y, a proce~s tha~ does not waste energy by he~ting th~ carbon-containin~, gas to a high te~perature as i~ an arc jet, while increasing the rat~ o~ deposition on a substrat~ as co~pared to the rat~ a~tained u~ing any known low te~perature ~ilent discharge prOCeSQ.
Accordi~g to the invention, a process for forming dia-mond coating~ in whîeh a plasma-producing gas~es or ~ixture 2~ ~ ~3~`~
of ga8es is pa~ed through a low te~perature ~ilent di~charge to generate a low temperature non-equilibrium plasma gas stream, the plasma ga~ ~tream i8 adiabatically e~panded into a region of lower pressure to for~ a pla~ma ga~ stream of highly ionized and di~sociated gase~ that i9 then directed on~o ~he ~ur~ace of a ~ubstrate, i characterized in that a carbon-con~aining 8as i~ injected into ~he high ~elocity plas~a ga~ 3tre~m during or after the expansion into a region of lower presaure.
~l~hough according to 8tati9tical m~chanics the ter~
temperature in a non-equilibrium plasma i8 not correct, the effective tsmperature of the plasma produced by the ~ilent discharge i9 regarded as being in the rang~ of 500 to about ~000~, preferably froM about 1300 to about 1800R. Th~se te~perature ranges achieve a degree of ionizatio~ and dis-~ociation very far out of equilibrium; in fact, to obtain the sa~e degree of ionization and dissociation thermodynami-cally, the ga8 would have to be h~ated to 8everal thousand degrees Kelvin. The low temperature, and the fact that nei-ther the carbon forming gas nor the product~ that are formedwhen it reacts with the scti~ated hydrog~n are e~posed to the di~charge ~inimlz~ the occurr~ce of unwanted side reaction~.
Th~ pla8ma-producing gas or ~lstur~ of gases that i8 initially ~re~t when ~he pla8~a i8 ~ormgd by the 8ilent di~char~ i8 hydrogen, either aloIie or in a ~i$ture o~ other gas~e8, whlch ~y include heliu~ or a~other iner~ ga~. The ine~t ga~ hely~ to ~abilize thQ discharge.
~he a~ou~t o~ th~ carbo~ co~ainin~ ga~ atded can be varied from about 0.1 to about 70 mol % of hydro~en depen-ding on whlch ga~ i8 used. For exa~ple, for methane the conc~ntra~ion i8 p~eferably from about 0.5 to 3 mol % based on the hydrog~n and for carbon monoxide it i~ preferably f ro~ about 10 to 40 mol % .
-5- 2 ~ ~ 4 3 ~ 7 Representative carbon containing ga~e~ include hydro-carbon~ containing one to four carbon ato~s such as methane, which is pre~erred, alcohol~ containing one to ~our carbon atoms, such as ethanol, and other o~ygen-eo~taining hydroear-bon~ containing one to ~our carbon ato~ such a8 acetone andcarbon monoxide. The mi2ture may a~so contain ~rom about 5 to about 30 mol 7., pref~rably about 10 mol %9 of the inert gas.
The proce~s can be carried out i~ 80m~ carbon-contain-ing gas is mi~ed ~ith the hydrogen, in which case the plasma produced by the discharge may initially already contain the activated protucts of a mixture of hydroge~ and 90me carbon-containing gas when the carbon con~aining gas i~ subseque~tly added in or downstream of the throat oi th~ nozzle.
Apparatus ~or producing a ~on-equilibriu~ pla~ma jet and the principles o~ its operation are alr~ady well known, ~or instance ~ro~ U.S. Patent 3,005,762. When relativèly low voltages up to a ~ew hundred volts are impressed on a pair o~ electrodes between which a gas i8 passing, a small current, on the order o~ ~icroamp~!res, i8 produced. A~ the voltage between the two electrod~ increases, the current al~o incr~a~es. The increase in curr~t ~low with ~oltage i8 at~ributable to a~ i~crea8c i~ th~ ~u~ber of ion~ and electro~s i~ th~ ~aa. A8 th~ applied volta~ increased ~till ~urth@r, th~ ~u~er o~ ~o~ continually increases, ~cr~a~ th~ ~low of current with little or no increase in volta~e. That region of increasing curre~t wi~h little cha~ voltage i8 the region o~ a ~low diseharge.
I* the a~plied`voltage i8 increased still ~urther in the regio~ o~ ~he ~low di~charge, whe~ a critical potential dif~erence i8 reach@d (uQually on the order of thou~and~ of volt~ and sp~cifically dep~nding upon the elec~rode distance, -6- 2 ~ 7 the chemical ~ature o~ the gas, and the pressure and temper-ature o~ the gas), a point i~ reached with increa~ing cur-rent at which there occur~ a sudden increase in current flow to the order of many amperes, the potential di~erence between the two electrodex drops to a fe~ volts, and there occur~ what i9 kno~n a8 a high-current arc. Ths arc i8 main-tained by copiouY e~isaion of electrons fro~ th~ cathode.
Thus in arc-producing devices the cathode deteriorate~ and has to be periodically replaced. A further problem i8 that par~iculat~ material from the cathode becomes a part of the plasma and a potential contaminant for any deposition ~ade by the pla~ma, which would destroy the u~ility o~ the coating for electro~ic applications.
The electrical discharge phenomena described can be lS brou~ht-about with either alternating or direct electric current. When alternating curre~t of suf~icient frequency i8 employed, the electrode~ do not need to be in contact with the dlscharged gas and may be ~eparated ~rom ~he dis-charge ~y a di~lectric mat~rial such as a quartz or PYR~X
tube. In ~uch cases, the current ~low in the ga3 occurs by induction and the resulting discharge i8 frequently termed an electrod~le~s dlscharge.
Sinc~ th~ pres~nt lnv~ntion u~es a low te~perature silent discharge, it o~ coursc relates only to the typc o~
low t~peratur~ p~oce~a~ alre~dy de3cribed (glow, corona, RF, ~cro~av~, ~lectrod~le~, a~d ozo~izer discharges occur-rin~ prio~ to 0~8et 0~ an arc), all op~ratet at lo~ curren~
de~t~o~ a~d hi3h volta~es. Tho curr~t densities are on th~ ord~ o~ ~illia~p~res ~o a~per~s per square centimeter, and the volta~es i~volved are o~ a relati~ly high magni-tude. Preferably, a dc glow di~chargc, a radio frequency ~rf~ discharge~ or a microwave discharge is u~ed to ac~ivate ~he ga~.
;
.
.
-7- 2~ ~3~
By introducing the gas into the discharge ehamber at relatively low velocity, where it i~ subject~d to th~ Qilen~
di~charge, non-equilibrium concentrations oP activated ~pe-cie~ are produced by the discharge with efficient utiliza-tion of energy a~d with relati~ely low ~ubstrate tempera-ture~ a high te~peratur~ arc discharæe ~ere to be u8e~, these advantag@s of the invention would be 108t.
In t~e dr3wings;
FIGUR~ 1 ~hows diagrammatically the basic apparatus ~or carrying out ~h~ proce~s o~ the invention when a dc glow di~charge i8 used to activate the gas.
FIGUR~ 2 shows diagrammatically an Q~bodiment of the apparatus for carryin~ out the process o~ th~ i~ve~ion, when ~ radio frequency (RF) di~eharge i8 U ed ~o activa~e lS the gas.
FIGUR~ 3 ~hows diagra~atically an embodiment of the apparatus ~or carryi~g out the inve~tion when a microwave discharge is us@d to activate the ~as.
Re~erence i~ made to FIG~RE :L, a schematic diagram o~
th~ basic arrangement o~ th~ apparatu~ ~or practicing the prese~ invent~o~. The hydrogen ~a~ or a misture o~
hydroge~ a~d other ga88e8 i8 introduced through a reactant input duct 8 lnto the discharg~ ch~ober 3. Th~ gA8 ~low 15 pa88~8 through a di~charg~ c~ er 3, throu~h an ~lectrical disehar~e lO, a~d through the ~oz~:le 2, to form a higher v~locity 3~ 11 that ~tri~es the alubstrate 7. The electri-cal ~char~ t~a~ convert~ the ga~ pa~sing through it lnto a plas~ produced by th~ appllcatio~ oP an electrical pote~tial ~ro~ po~r ~upply 17, through eleetrical ~eed line~ 13 and 14 across the gap betwee~ the electrode 1, and the nozzle 2, which acts as the o~her discharge electrode.
Th~ power ~upply 17 may produce an alternating or direct curr~nt.
-8- 2 ~ 3 ~ 7 I~ alternating curre~t i~ used. and it i desired to u~e an electrodele~s di charge, a well known and ~impl~
modification o~ the the di~charge chamber 3 can be made hy incorporating o~ a dielectric material such as a quartz or PYRE~ tube, so that the current flow in the gas occur~ by induction through that material.
Conventionally, ~he m~tal of the ~lectrodes ca~ be of variou~ ki~ds bu~ ~hould have high thermal conduc~ivity. A~
high-current den~ities, or whe~ ~etal~ of lower melting points, such as copper or aluminum, are employed, it may be nece~sary to cool the electrodes conventionally, such as by clrculation o~ a ~luid such as water through channels in the electrodes. I~ ca~e8 where the coolan~ lee~rically con-ductiv~, a suffici@ntly long path through ~on-conductire 15 tubing must: be provided for the coolant o any non-grounded eleetrode, 1 or 2, i~ order to pre~e~t lea~age of electric current through the coola~t to the ground.
The optimuM pressure in the discharge chamber depends upon a nu~ber of fac-tors such as electrode di3tance and ~0 shape, power ~upply voltage, ~he .nature of the gas, and the ~r~quency of the curre~t when an laIter~ating current ia employed. At low frequ~ncies or ~with direct.current, it i9 usually desirabl~ to have th~ diseharge chamber 3 at a pres-~ure ~rolo about 1.333 ~l?a to about 101.324 ~cPa (about 10 to 25 about 760 torr), pre~rably ~ro~ bout 4 ~Pa to about 53.328 l~Pa (about 30 to about 400 torr ) .
Th~ nozzle 2 prov~de~ a mea~s of e~rpandl~g the plasma ~ro~ 'ch~ discharge chaluber 3 in~o the e~ansion or depo~ition cha~r 4. Th~ pla~ma ~lows through the nozzle 2 and i8 30 accelerated, b~ause o~ th~ pr~ssure drop between the di~-charg~ chamber 3 alld ~h~ e~pan~ion chamber 4, to a higher velo~ity a~ a reduced tempera~ure. The temperature of the e~pa~ded plas~a jet a~ it pa~se~ i~to the expansion chamber 4 2~ ~3~
_9_ can be estimated from the pre~Yure ratio:
/ PE \~
T~c~ TDC
~PDCJ
where TDC i~ the ga~ dyna~ic temperature i~ the discharge chamber, TEC i8 the te~perature o~ the jet in the e~pa~sion chamber, and PDC and P~C are the pressure in the discharge chamber and the e~pan~ion chamber, respectively. The temper ature i~ the discharge chamber i~ e~timated from the pressure increa~e when the discharge i9 tur~ed o~. The pre#sure in the e~pa~sion cha~ber 4 i~ alwaya maintained at a value le38 than that i~ the discharge chamber 3, and i8 generally from abQUt 0.1332 ~Pa to about 13.3322 kPa ~about 1 to abou~ 100 torr), pre~erably fro~ about 0.666.1 kPa to abou~ 6.661 kPa (about 5 tv about S0 torr). I~ this e~bodi~ent a vacuum pu~p, not shown, i8 connected to th~ expan3ion cha~ber 4 through an exhau~t duct 16 containing a ~uitable con~entional means for the re~ulation o~ pre~ure wit~in the e~annio~ chamber 4.
The area o~ the throat o~ the nozzle 2 i8 principally determined by the velocity that i~ d~sired i~ the jet a~ it ~trikes the sub~tratel and the ~a8B rate o~ flow of gas de~ired. They are de~er~ined by the dim~nsions og the ~ubstrate to b~ treated and i~ orie~ta~ion ~o the ~tream.
The~e ~actoss can b~ va~ied over ~id~ ran~eo according to well ~own co~v~tio~al principle~.
~ hl8h @~ou~h pre~u~e ratios ar~ em~loyed, the jet velociti~ may ~each sevesal time~ the local ~p~ed o~ ~ound i~ th~ ~a~. Thu8, ~elocitie~ on th~ ordcr o~ thou~ands o~
~ee~ ~r s~co~d ~ay be o~ai~ed, de~ending upon ~he molecular w~igh~ a~d speei~ic h~at ra~ios o~ the gas, its i~i~ial tem-pesatur~ prior to e~pan~ion, a~d the pre~ure ratio existing between th@ two chamb~r3.
2~ 3~
Pre~erably, the con~truction of the nozzle 2 i~ ~uch a~
to impart 80nic, or supersonic, velocitiea to the reactive ga~, ~o a~ to incr@a~e the velocity and thuQ the rate of depo-sition, while reducing the time a~ailable for the reactants to decay. After expansion, the pla~a jet will typically have a temperature in the range of from about 25Q~ to 1800OK, and more pre~erably i~ 250~ to 1400~.
Pre~erably, a~ in the e~bodiment illus~rated, the carbon con~aini~g gas is introduced in the ~xit section of the nozzle down~tream of the nozzle throat 18 (the 8malle8t diameter o~
the nozzle) through i~put ducts 9 connected to a plurality of orifices 12, to rapidly mis with the plasma 10 produced by the di~charge to ~or~ the plasma jet 11. The velocity og the injected gas i~ ~ainly determined by the pre~sure drop across the orificea 12.
The p:La~ jet 11 i8 directed 80 that it contacts a sub-strate 7. The substrate i~ positioned in the expansion chamber 4 using a ~ubstrate holder S, moun~ed on a position-ing rod 6 that allow~ move~e~t of th~ ~ub~trate towards or away ~ro~ the nozzle 2, The ~ubstrate wlll generally be located ~ro~ about 2 to 30 cm, pre~erably ~ro~ about 6 to lO
c~ ~ro~ the nozzl~.
The rela~ively hi~h te~peraturs o~ the plas~a and the velocity o$ th~ plas~a jet wh2n it i~pi~g~s on th~ substrate 2S will heat th~ ~ubstrat~ to te~peratu~es v~ry clos~ to the temperature~ i~ the discharge cha~b~r 3. This occur~ becau~e th~ ra~do~ e~erg~ that d~fine~ t@~perature ha~ been converted to dir~cted ~ergy, high ga~ velocity, i~ the dow~rea~ ec-tio~ o~ th~ no~zle, ~ImNltaneou~ly causing a decrea~e in ga~
te~pera ure. When this ~et ~tri~es the substrate, the ga~
jet i8 sudde~ly stopped a~d the directed energy returned to random energy ~hrough a shock wave that i3 produced in front of the 3ubstrate. The energy iY congerv@d.
. . . ~
.
:: .
' `
In high temperature di~charge , such as electrical arc~, the concentration of activated ~pecies require~ a thermodyna~ic equilibrium favoring the activated product.
In ord~r to produce a significant amount of acti~ted ~pecie~, e~tremely high temperatures, e.g. temperatures o~
at lea~t 4000R are required. Temperatures as high aQ
10,000 to 30,000K may be u~ed, which mean~ that most of the heat is u3ed to heat the ga~, a great amount of power iQ
required, and the ~ub trate i8 heated to the e~tent that graphi~e and a~orphous carbon may b~ ~ormed instead of dia-~ond, and e~en to the e~tent that the substrate may b~
destroyed, unless the ~ub~trate i8 cooled. Problem~ a8~0-ciated with the th~rmal stability o~ the substrate and di~ference~ between the coef~icient~ of expan~ion o~ the ~ubatrate and the depo~ited diamond film li~i~ the types o~
sub3trate~ that can be used.
For in~tance, in a high tem~eratur~ ~yate~ de~cribed in ~urihara et al., A~ bY~. Le~ 2(6) 19:pp 437 and 438 (1988) and in ~uropean Patent App~ication 0286306 a thermal plasma i8 ~or~ed by passing a mi~:ur~ og methane and hydro-gen through an arc discharge and i~jecting methane into ~he area o~ th~ arc or below it. Tho plas~a i8 pa~ed through a nozzle, espanded to precipitate da~ond and ~inally directed onto a 8ub~trat~ rihara e~ al. 8u~e8t that the problem of ~o~ 8 graphite or amorphous carbon on the substrate becau~ o~ th~ h~gh te~peratures ca~ b~ o~erco~e by w~ter-coolln~ the ~ubstrate.
~ thod~ ~or pr~paring diamond ellm~ that do not require a ther~odyn~ic equilibrium ~àvoring the aetivated produc~, that 13t by ge~ra~in~ a low tem~erature no~-equilibri~
plasm~ for ch~ical vapor depo~ition, have been de~cribed.
Low temperature discharges, include glow di~charges, corona~, electrodeles~ di~charges, and ozonizer di~charge~, as well a~ ~o~ RF and ~icrowave di~charges9 are ganerically ~nown 2~3~7 as a8 "~ilent discharges". Chemical activation in low temperature 8y8te~8 results in a non-equilibrium produc~ o~
the activated species. The concentration of ions and free radical~ in such plasma~ i~ much greater than would be expected on the basis o~ ~h~rmal equilibrium con~iderations.
The use o~ a non-equilibrium plasma jet in a di~ferent conte~t i8 describ~d in a report entitled ~Synth@~is of Silane and Silicon in a Non-equilibrium Plasma J@t", authored by H. F. Caleote (~.S. Department o~ Energy/Jet Propulsion Laboratory Report 954560-76/8), which di3clos~
~orming the plasma by a DC discharge, sub~equently expanding it through a nozzle to form a plasma jet, and directing the jet upon a substrate to prepare adh~rent 8ilicon films.
The u~e of a low temperature plas~a produced by passing a mixture o~ plasma-producing gasses, incluting a carbon-con-taining ~a~, through a glow di~charge to ~orm diamond coat-ings i~ ~u~ested in ~.S. P~tent No. 4,767,~08, but the pro-cess it di~close~ as being useful actually forms a high tem-perature plasma CVD by using an electric arc discharge to decompo~e a carbon 80urce and g~nerate a plasDa gas contain-ing carbo~ ions or carbon radicals. The plasma g~8 i8 ~ubse-quently adi~batically espanded the to precipitate diamond on a 8ubatrate. Since t~s patent al80 Btate~ that the proces~
U8~g a low temp~rature plasma results ~n a very 810~ rate o~ dia~ond ggowt~, it strongly ~ug~est~ that an~ one o~ the low te~pera~ur~ proce~ses i~ ~ot ~fective.
Th~ i8 a need for a di~Xere~t approach to Porming dia-`mond coati~gs, name~y, a proce~s tha~ does not waste energy by he~ting th~ carbon-containin~, gas to a high te~perature as i~ an arc jet, while increasing the rat~ o~ deposition on a substrat~ as co~pared to the rat~ a~tained u~ing any known low te~perature ~ilent discharge prOCeSQ.
Accordi~g to the invention, a process for forming dia-mond coating~ in whîeh a plasma-producing gas~es or ~ixture 2~ ~ ~3~`~
of ga8es is pa~ed through a low te~perature ~ilent di~charge to generate a low temperature non-equilibrium plasma gas stream, the plasma ga~ ~tream i8 adiabatically e~panded into a region of lower pressure to for~ a pla~ma ga~ stream of highly ionized and di~sociated gase~ that i9 then directed on~o ~he ~ur~ace of a ~ubstrate, i characterized in that a carbon-con~aining 8as i~ injected into ~he high ~elocity plas~a ga~ 3tre~m during or after the expansion into a region of lower presaure.
~l~hough according to 8tati9tical m~chanics the ter~
temperature in a non-equilibrium plasma i8 not correct, the effective tsmperature of the plasma produced by the ~ilent discharge i9 regarded as being in the rang~ of 500 to about ~000~, preferably froM about 1300 to about 1800R. Th~se te~perature ranges achieve a degree of ionizatio~ and dis-~ociation very far out of equilibrium; in fact, to obtain the sa~e degree of ionization and dissociation thermodynami-cally, the ga8 would have to be h~ated to 8everal thousand degrees Kelvin. The low temperature, and the fact that nei-ther the carbon forming gas nor the product~ that are formedwhen it reacts with the scti~ated hydrog~n are e~posed to the di~charge ~inimlz~ the occurr~ce of unwanted side reaction~.
Th~ pla8ma-producing gas or ~lstur~ of gases that i8 initially ~re~t when ~he pla8~a i8 ~ormgd by the 8ilent di~char~ i8 hydrogen, either aloIie or in a ~i$ture o~ other gas~e8, whlch ~y include heliu~ or a~other iner~ ga~. The ine~t ga~ hely~ to ~abilize thQ discharge.
~he a~ou~t o~ th~ carbo~ co~ainin~ ga~ atded can be varied from about 0.1 to about 70 mol % of hydro~en depen-ding on whlch ga~ i8 used. For exa~ple, for methane the conc~ntra~ion i8 p~eferably from about 0.5 to 3 mol % based on the hydrog~n and for carbon monoxide it i~ preferably f ro~ about 10 to 40 mol % .
-5- 2 ~ ~ 4 3 ~ 7 Representative carbon containing ga~e~ include hydro-carbon~ containing one to four carbon ato~s such as methane, which is pre~erred, alcohol~ containing one to ~our carbon atoms, such as ethanol, and other o~ygen-eo~taining hydroear-bon~ containing one to ~our carbon ato~ such a8 acetone andcarbon monoxide. The mi2ture may a~so contain ~rom about 5 to about 30 mol 7., pref~rably about 10 mol %9 of the inert gas.
The proce~s can be carried out i~ 80m~ carbon-contain-ing gas is mi~ed ~ith the hydrogen, in which case the plasma produced by the discharge may initially already contain the activated protucts of a mixture of hydroge~ and 90me carbon-containing gas when the carbon con~aining gas i~ subseque~tly added in or downstream of the throat oi th~ nozzle.
Apparatus ~or producing a ~on-equilibriu~ pla~ma jet and the principles o~ its operation are alr~ady well known, ~or instance ~ro~ U.S. Patent 3,005,762. When relativèly low voltages up to a ~ew hundred volts are impressed on a pair o~ electrodes between which a gas i8 passing, a small current, on the order o~ ~icroamp~!res, i8 produced. A~ the voltage between the two electrod~ increases, the current al~o incr~a~es. The increase in curr~t ~low with ~oltage i8 at~ributable to a~ i~crea8c i~ th~ ~u~ber of ion~ and electro~s i~ th~ ~aa. A8 th~ applied volta~ increased ~till ~urth@r, th~ ~u~er o~ ~o~ continually increases, ~cr~a~ th~ ~low of current with little or no increase in volta~e. That region of increasing curre~t wi~h little cha~ voltage i8 the region o~ a ~low diseharge.
I* the a~plied`voltage i8 increased still ~urther in the regio~ o~ ~he ~low di~charge, whe~ a critical potential dif~erence i8 reach@d (uQually on the order of thou~and~ of volt~ and sp~cifically dep~nding upon the elec~rode distance, -6- 2 ~ 7 the chemical ~ature o~ the gas, and the pressure and temper-ature o~ the gas), a point i~ reached with increa~ing cur-rent at which there occur~ a sudden increase in current flow to the order of many amperes, the potential di~erence between the two electrodex drops to a fe~ volts, and there occur~ what i9 kno~n a8 a high-current arc. Ths arc i8 main-tained by copiouY e~isaion of electrons fro~ th~ cathode.
Thus in arc-producing devices the cathode deteriorate~ and has to be periodically replaced. A further problem i8 that par~iculat~ material from the cathode becomes a part of the plasma and a potential contaminant for any deposition ~ade by the pla~ma, which would destroy the u~ility o~ the coating for electro~ic applications.
The electrical discharge phenomena described can be lS brou~ht-about with either alternating or direct electric current. When alternating curre~t of suf~icient frequency i8 employed, the electrode~ do not need to be in contact with the dlscharged gas and may be ~eparated ~rom ~he dis-charge ~y a di~lectric mat~rial such as a quartz or PYR~X
tube. In ~uch cases, the current ~low in the ga3 occurs by induction and the resulting discharge i8 frequently termed an electrod~le~s dlscharge.
Sinc~ th~ pres~nt lnv~ntion u~es a low te~perature silent discharge, it o~ coursc relates only to the typc o~
low t~peratur~ p~oce~a~ alre~dy de3cribed (glow, corona, RF, ~cro~av~, ~lectrod~le~, a~d ozo~izer discharges occur-rin~ prio~ to 0~8et 0~ an arc), all op~ratet at lo~ curren~
de~t~o~ a~d hi3h volta~es. Tho curr~t densities are on th~ ord~ o~ ~illia~p~res ~o a~per~s per square centimeter, and the volta~es i~volved are o~ a relati~ly high magni-tude. Preferably, a dc glow di~chargc, a radio frequency ~rf~ discharge~ or a microwave discharge is u~ed to ac~ivate ~he ga~.
;
.
.
-7- 2~ ~3~
By introducing the gas into the discharge ehamber at relatively low velocity, where it i~ subject~d to th~ Qilen~
di~charge, non-equilibrium concentrations oP activated ~pe-cie~ are produced by the discharge with efficient utiliza-tion of energy a~d with relati~ely low ~ubstrate tempera-ture~ a high te~peratur~ arc discharæe ~ere to be u8e~, these advantag@s of the invention would be 108t.
In t~e dr3wings;
FIGUR~ 1 ~hows diagrammatically the basic apparatus ~or carrying out ~h~ proce~s o~ the invention when a dc glow di~charge i8 used to activate the gas.
FIGUR~ 2 shows diagrammatically an Q~bodiment of the apparatus for carryin~ out the process o~ th~ i~ve~ion, when ~ radio frequency (RF) di~eharge i8 U ed ~o activa~e lS the gas.
FIGUR~ 3 ~hows diagra~atically an embodiment of the apparatus ~or carryi~g out the inve~tion when a microwave discharge is us@d to activate the ~as.
Re~erence i~ made to FIG~RE :L, a schematic diagram o~
th~ basic arrangement o~ th~ apparatu~ ~or practicing the prese~ invent~o~. The hydrogen ~a~ or a misture o~
hydroge~ a~d other ga88e8 i8 introduced through a reactant input duct 8 lnto the discharg~ ch~ober 3. Th~ gA8 ~low 15 pa88~8 through a di~charg~ c~ er 3, throu~h an ~lectrical disehar~e lO, a~d through the ~oz~:le 2, to form a higher v~locity 3~ 11 that ~tri~es the alubstrate 7. The electri-cal ~char~ t~a~ convert~ the ga~ pa~sing through it lnto a plas~ produced by th~ appllcatio~ oP an electrical pote~tial ~ro~ po~r ~upply 17, through eleetrical ~eed line~ 13 and 14 across the gap betwee~ the electrode 1, and the nozzle 2, which acts as the o~her discharge electrode.
Th~ power ~upply 17 may produce an alternating or direct curr~nt.
-8- 2 ~ 3 ~ 7 I~ alternating curre~t i~ used. and it i desired to u~e an electrodele~s di charge, a well known and ~impl~
modification o~ the the di~charge chamber 3 can be made hy incorporating o~ a dielectric material such as a quartz or PYRE~ tube, so that the current flow in the gas occur~ by induction through that material.
Conventionally, ~he m~tal of the ~lectrodes ca~ be of variou~ ki~ds bu~ ~hould have high thermal conduc~ivity. A~
high-current den~ities, or whe~ ~etal~ of lower melting points, such as copper or aluminum, are employed, it may be nece~sary to cool the electrodes conventionally, such as by clrculation o~ a ~luid such as water through channels in the electrodes. I~ ca~e8 where the coolan~ lee~rically con-ductiv~, a suffici@ntly long path through ~on-conductire 15 tubing must: be provided for the coolant o any non-grounded eleetrode, 1 or 2, i~ order to pre~e~t lea~age of electric current through the coola~t to the ground.
The optimuM pressure in the discharge chamber depends upon a nu~ber of fac-tors such as electrode di3tance and ~0 shape, power ~upply voltage, ~he .nature of the gas, and the ~r~quency of the curre~t when an laIter~ating current ia employed. At low frequ~ncies or ~with direct.current, it i9 usually desirabl~ to have th~ diseharge chamber 3 at a pres-~ure ~rolo about 1.333 ~l?a to about 101.324 ~cPa (about 10 to 25 about 760 torr), pre~rably ~ro~ bout 4 ~Pa to about 53.328 l~Pa (about 30 to about 400 torr ) .
Th~ nozzle 2 prov~de~ a mea~s of e~rpandl~g the plasma ~ro~ 'ch~ discharge chaluber 3 in~o the e~ansion or depo~ition cha~r 4. Th~ pla~ma ~lows through the nozzle 2 and i8 30 accelerated, b~ause o~ th~ pr~ssure drop between the di~-charg~ chamber 3 alld ~h~ e~pan~ion chamber 4, to a higher velo~ity a~ a reduced tempera~ure. The temperature of the e~pa~ded plas~a jet a~ it pa~se~ i~to the expansion chamber 4 2~ ~3~
_9_ can be estimated from the pre~Yure ratio:
/ PE \~
T~c~ TDC
~PDCJ
where TDC i~ the ga~ dyna~ic temperature i~ the discharge chamber, TEC i8 the te~perature o~ the jet in the e~pa~sion chamber, and PDC and P~C are the pressure in the discharge chamber and the e~pan~ion chamber, respectively. The temper ature i~ the discharge chamber i~ e~timated from the pressure increa~e when the discharge i9 tur~ed o~. The pre#sure in the e~pa~sion cha~ber 4 i~ alwaya maintained at a value le38 than that i~ the discharge chamber 3, and i8 generally from abQUt 0.1332 ~Pa to about 13.3322 kPa ~about 1 to abou~ 100 torr), pre~erably fro~ about 0.666.1 kPa to abou~ 6.661 kPa (about 5 tv about S0 torr). I~ this e~bodi~ent a vacuum pu~p, not shown, i8 connected to th~ expan3ion cha~ber 4 through an exhau~t duct 16 containing a ~uitable con~entional means for the re~ulation o~ pre~ure wit~in the e~annio~ chamber 4.
The area o~ the throat o~ the nozzle 2 i8 principally determined by the velocity that i~ d~sired i~ the jet a~ it ~trikes the sub~tratel and the ~a8B rate o~ flow of gas de~ired. They are de~er~ined by the dim~nsions og the ~ubstrate to b~ treated and i~ orie~ta~ion ~o the ~tream.
The~e ~actoss can b~ va~ied over ~id~ ran~eo according to well ~own co~v~tio~al principle~.
~ hl8h @~ou~h pre~u~e ratios ar~ em~loyed, the jet velociti~ may ~each sevesal time~ the local ~p~ed o~ ~ound i~ th~ ~a~. Thu8, ~elocitie~ on th~ ordcr o~ thou~ands o~
~ee~ ~r s~co~d ~ay be o~ai~ed, de~ending upon ~he molecular w~igh~ a~d speei~ic h~at ra~ios o~ the gas, its i~i~ial tem-pesatur~ prior to e~pan~ion, a~d the pre~ure ratio existing between th@ two chamb~r3.
2~ 3~
Pre~erably, the con~truction of the nozzle 2 i~ ~uch a~
to impart 80nic, or supersonic, velocitiea to the reactive ga~, ~o a~ to incr@a~e the velocity and thuQ the rate of depo-sition, while reducing the time a~ailable for the reactants to decay. After expansion, the pla~a jet will typically have a temperature in the range of from about 25Q~ to 1800OK, and more pre~erably i~ 250~ to 1400~.
Pre~erably, a~ in the e~bodiment illus~rated, the carbon con~aini~g gas is introduced in the ~xit section of the nozzle down~tream of the nozzle throat 18 (the 8malle8t diameter o~
the nozzle) through i~put ducts 9 connected to a plurality of orifices 12, to rapidly mis with the plasma 10 produced by the di~charge to ~or~ the plasma jet 11. The velocity og the injected gas i~ ~ainly determined by the pre~sure drop across the orificea 12.
The p:La~ jet 11 i8 directed 80 that it contacts a sub-strate 7. The substrate i~ positioned in the expansion chamber 4 using a ~ubstrate holder S, moun~ed on a position-ing rod 6 that allow~ move~e~t of th~ ~ub~trate towards or away ~ro~ the nozzle 2, The ~ubstrate wlll generally be located ~ro~ about 2 to 30 cm, pre~erably ~ro~ about 6 to lO
c~ ~ro~ the nozzl~.
The rela~ively hi~h te~peraturs o~ the plas~a and the velocity o$ th~ plas~a jet wh2n it i~pi~g~s on th~ substrate 2S will heat th~ ~ubstrat~ to te~peratu~es v~ry clos~ to the temperature~ i~ the discharge cha~b~r 3. This occur~ becau~e th~ ra~do~ e~erg~ that d~fine~ t@~perature ha~ been converted to dir~cted ~ergy, high ga~ velocity, i~ the dow~rea~ ec-tio~ o~ th~ no~zle, ~ImNltaneou~ly causing a decrea~e in ga~
te~pera ure. When this ~et ~tri~es the substrate, the ga~
jet i8 sudde~ly stopped a~d the directed energy returned to random energy ~hrough a shock wave that i3 produced in front of the 3ubstrate. The energy iY congerv@d.
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3 ~ ~
Consequ~ntly, under ~ome conditiolls of operation, it may be nece~ary to cool the ~ub~trate, ~o that the ~ub~trate holder may be provided with cooling means, not shown. Ths substrat@ i~ preferably maintained at a temperature between 300 and 1100K. ~nder other conditions of operation, it may be de3ira~1e to 3upply additional heat to the substrate, ~o that the ~ub~trate holder may be proYided with conventional mean~ ~or heating the substrate, not shown.
Pre~erably, the substrate will be oriented sub~tantially perpendicular to the flow o~ the plasma jet. This will tend to maximize the rate o~ deposition of the diamond coating.
However, the substrate holder may be provided with means for pivoting the sub~trate 80 that the area that i8 contacted may be changed from a circle to an oval, thus i~creasing the coating area.
Reference i8 made to ~IGURE 2, which shows an embodiment employing a radio ~requency (r~) electrical di~charge ~o acti-vate the gas, instead o~ the dc discharge de~cribed above.
Power supply 17 of Fig. 1 i~ replalced by a radio ~requency power supply 19 and th~ electrical lead~ 13 and 14 are replaced by el~ctrical leads 20 al~d 21 which may then be coaxial cables to reduce electricall 108~ when higher rf ~requencies ar~ employed. Dischas~g~ cha~ber 3 o~ Fig. 1 i~
replaced by di scharg~ chamber 22 D~ad~ o~ a nonconducting sub#ta~c~ . guar~z or ~YRE~ a~d 18 ~u~rounded by an rf coil 2~. Th~ di~aion~ and nu~r of tus~ in coil 23 con~e~o~ally depend upoa th~ ~reque~cy ~nd impedence requir~ ts of th~ r~ power supply 19. This will be readily deter~in~d by o~e a~illed in ~he a~t. A~ higher powe~ level~
it will be nece~ary to cool coil 23, by pa88ing a cooling ~luid such a~ ~ater through it (not shown in the figure~.
Whe~ a conducting ~luit i~ u~ed it will have to be i~olated from electrical ground, e.g. by passin~ it through a long length of nonconducting tubing 80 that th~ length of 2~3~
conducting liquid used ha3 a high electrical re~ista~ce to ground. The rf power i8 inductively coupled to the gas pa~s-ing through the discharge chamber 22 producing a~ rf electri-cal di~charge lnside chamber 22. This type o~ dischar~e avoids eleetrode~ being in contact with the gas and is thus use~ul when unusually pure dia~ond~ are required, for instance ~or use in semiconductors. All o~her component~ in Figure 2 are the same as those identified in Figure 1.
In another embodiment of the invention, as shown in Figure 3, ~he electrical power that ac~ivates the ga~ i8 furnished by a microwave power supply 24 coupled to the di~-charge chamber 25 th~ou~h an appropriate wave guide 26 and coupling device 27. The dîscharge ~ha~ber 25 also ~erves as a ~icrowave resonant cavity 80 that the hlgh el~ctro~a~ne~ie ~ields created therein ionize the gas ~ed to chamb~r 25 through ~eed line 28 to create a plasma. Also shown i~ ring injector 29, which ~erve8 to direet and concentrate the car-bon-containin8 gab 80 that a high~r proportio~ of the gas contacts the sub~trate. Although not shown in F~gures 1 and 2, a ring injector can be employecl in the apparatus shown in tho~e Figure~ ~o~ the same purpose!. The ri~g injector 29 may also be us~d to in~eet an additiorlal roacta~t gaa downstream o~ th~ noz21~. Thi8 e~bodiment allow8 the sub8trate to be positio~ed furth~ ~ro~ th~ no2~ hi~ retalning the abil-ity to adju~t t~ substrate-to-no2;zle tista~c~ independ~n~ly o~ th~ di~tanc~ between the ~ub~trate and th~ poin~ of do~n-~trea~ ctio~. Thi~ ~leæi~ility allow~ for g~eater con-trol of p~ocosæ p~raMcters leading to optimization of diamond growt~ co~dition~. All other compo~ent8 o~ Figure 3 are the ~a~e as tho8e identified in Figure 1.
Representative ~ubstrate~ include silicon, nickel, gal-liu~ ar~nide, titanium, copper, copper-carbon composite, alu~inu~ ni~ride, ~ilicon carbide, aluminu~-silicon-carbon , .
2~ ~3~
compo~ite, alumina, molybdenum, gold, ~pinel, ?ilica, tung-sten, graphite, copper-tung~1:en alloys and 8 licon-iron.
Surpri~ingly, the proces~ according to the invention results in the produetion of diamond coatings on the sub-5 strate, in~t~ad of any of the many other form~ o~ carbon suchas graphite, amorphoua carbon, hydrogenated carbon, gla88y carbon or oth~r carbon allotropes. Thi3 i8 con~.irmed by Raman ~pec~ro copy, i~ the ~ollowing ~s~ples, with the characteristic dia~ond peak seen a~ about 1332 cm 1, The 19 esact location of the peak i8 determined by a number o~ fac-tors, e.g. ~he strain between the f ilm and the substrate.
The purity o~ the dia~ond deposit i8 indicated by the heigh~
o~ the scatt~red Raman pea~ and the peak width. A diamont quality factor, Q, i8 used herein to refer to the ratio o~
the peak intensity above the underlying continuum to the intensity o~ the u~derlaying co~tinuu~ above the minimum in the baaeline in the range o~ 500 to 1700 c~-l. Thi~
continuum i8 probably aasociated with graphitle, which has a ~catt~ring e~iciency about 100 times that of diamond. Qual-ity ~actorn a~ high as 27 hav~ b~n observed. It i8 to beunders~ood, how~ver, that a~ in natural dia~onds, 3mall a~ount~ o~ i~purities, ~uch a~ hy~drogen, ~it-rogen or silicon may be pre~ent. In ~o~e ~bodiments it ~ay actually be de3irable to lntroduce llimpuritle81', such as when the diamond coating i~ dop~ to for~ p- and ~-type material8.
Th~ apl?~r~tus show in Figur~ 1 was opera~d ~or 6 hour~
at a~ applied voltage o~ 109S voïts and current o~ 2.0 ampe~e~, ~ith a discharge power o:~ 2200 W while ~eeding hydro-30 gen at 23.7 ~ole/s and hellu~ at 2.37 ~ole/s through feedline 8. Methane was a~ded at 0.13 mmole/s in the nozzle through fe~d lin~ 9 and orifice~ 1~. The pre~ure in the plas~a chamber wa~ 127 torr and that in the depo~ition cha~nber was 17 torr. The discharge gas ~emperature wa about 2 ~ -7 ~
; 14--1600~: and the e:i~panded jet temperature was 900~:. A ~ilicon ~ubstrate, 8 cm down~tream o~ the nozzle, wa~ maintained at a temperature o~ 1100Q~ by the addition of 200 watts of electri-cal energy to the ~ubstrate holder 5 . A diamond f ilm h~ving 5 an average thickn@ss o~ 1-2 micron~ was de~o3ited over the entire 16 csll2 expo~ed surface of the sub~trate. A Raman spectrum of the fil~ e~hibitet the diamond feature at 1332 cn~~ on an underlying continuum oi~ comparable magnitude.
~-ray di~fraction analyRis o~ the ~ilm confirmed the presence 10 of crystalline diamond with 30me a-SiC at the interface.
There was no indication of the pre~ence of graphite, yet the Q was only 0.51.
~X~I~ .2 Rytro~e~, helium, and o~cygen, a~ the respec~ive flow 15 rate~ of 23 . 7, 2 . 37, 0 . 024 ~ole/~ were fet to ~he di charge in Figure 1 through ~eed line 8. A silicon sub~trate main-tained at about lOOO-K was positioned at a 30- angle to the jet a~i8 7 c~ ~rom the nozzle. W~th the di6charge opera~ing at 2360 W, 1180 volt~ and 2 amperes, the discharge gas temper-20 ature was 1640 R. Mathane was added at 0 . 39 ~ole/ 8 to thejet through a ring injector locat~d 2 cm down~tream of the nozzla, a~ th~l3 abov~ condition~ for 305 min. A diamont film having a mea~l thic~ over a 6 cla2 area of û.6 ~lcrons wa6 p~oduc~d on the~ ~ubstrate. Th~ a ga~e a ~s~an spec- -25 truls with 1:b~ ond feature ~ear 133~ ~-1 with a quality ~aetor, Q a 22.
E~ ` .
A ~olybd~u~ substrate was ~aai~talned at a t~pera~ure o~ 940-1~ (by h~ati~ el~ctrically) at a di~tance o~ 9 cm 30 rro~ the noz~l~ Or ~h~ apparatu~ ~hown in Figure 1. ~ydrog@n and heliula gas~s were f~d at respec~ive flows of 23 . 7 and 2 . 37 ~ole/~ to th~ discharge through feed liIle 8. While operating the discharge at 2500 W and 228 torr, me~hane was added aLt O . 39 ~mol~/s to the downstreala je~: through ~eed line 9 . This 2 ~ 1 ~ 3 6 7 re~ulted i~ a discharge gas temperature of 2330~K and an expanded jet temperature o~ 1170K~ Operation at these con-dition~ for one ~our r@sulted i~ production of a 16 cm2 diamond film covering the espoged ~urface of the substrate and having a ma~i~u~ thickness of 2-3 microns. A Raman ~pectrum o~ th~ ~ilm exhibited the diamond ~eature at 1334 ~AMPL~ 4 In-a ~imilar experiment to that d~scribed in E~ample 5, a molybdenum ~ubstrate was maintained at a temperature of 1065~. by electrical heating at a di~tance o~ 9 cm from the nozzle of the apparatu~ ~hown in Fig. 1. ~ydrogen and helium gases were ~ed at respective ~lows of 23.7 and 2.37 ~mole/s to the discharg~ through feed line 8. While operating the di3charg~ at 2500 W and 228 torr, a mi~rture of 0 . 77 ~ ole/~
o~ methane and 0.08 m~ole~/s of o~ygen were added to the ~ownstrea~ j~t through feed line 9. Operation st the~e condi-tions for on~ hour resulted in production o~ a 16 cm2 dia-mond film covering the espo3ed ~urface of the subs~rate and having an avera~e fil~ thickness o~ 4-5 ~icrons. A Raman spectrum o~ the ~ e~hib~t~d th~ diamond feature at 1338 c~
In a ~i~ilar ~p~rim~nt tho appa~atus o~ Figure 1 waa u~ed e~cept ~o ~ner~y ~as applied to ~he sub~tra~e holder which was allow~d ~o 8@~ it~ ow~ te~p~ratur~, 815~. Th~
sub~t~at~ ~a~ ~uaxtz ~lseed 7.5 c~ ~ro~ t~e noz~l~ esi~, hydro~e~ a~d h~liu~ were ~ed throu~h the di~charge at 23.7 a~d 2.3~ ~ole/~ respectively, 0.39 m~ole/s o~ ~ethane were injected i~o the nozzle e~i~ section through ~eed line 9, and the discharge was operated at 2l8o watt3 at a total 30 pressure o~ 139 ~orr. Thi~ r~sulted in a discharg~ gas temperature o~ 1600~ and an e~pa~ded jet temperature of 8600g. The pre3sure i~ ~h~ deposi~ion cha~b~r wa~ 17.4 torr. A dia~o~d ~il~ was deposi~ed as i~dicated by the Raman peak with a quality factor o~ 2.8.
2~ ~ ~3~
~ 6 I~ a~oth~r e~periment using the apparatus ~hown in Fig-ure l, a molybdenum ~ubstrate was h@ld 9 cm ~rom the nozzle exit, and wa3 heated only by energy from the do~nstream jet 5 expanding ~ro~ an up~trea~ pres~ure of 224 torr into the depo3ition chamber at a pre~sure of 17 torr. Feeding a mixture o~ hydroge~ at 23.7 mmole/s and heliu~ at 2.37 m~ole/~ throu~h line U to the discharge operat~d at 2050 W, and feeting methane to the downgtream jet at 0.39 mmole/~
through line 9, resulted in a subsgrate temperature of 71SK. Operation in this ~a~ner for 8 hours produced a dia~ond film on the substrate as evidenced by a character-istic Rama~ f@ature at 1333 cm 1 w~th a quality ~actor greater than 1.
~3~PLE_7 In an experi~ent using the app~ratu~ shown in Figure 1, a silicon substrate was held 11 c~ ~rom the nozzle e2it at a 30 degree angle relative to the jet and wa~ heated only by energy ~ro~ ~h~ down~tream jet e3~a~ding ~rom an upstream pressure o~ 140 Torr into the deposition cha~ber at a pre~-sure o~ 18 Torr. A oli~cture o~ hydrogen at 23~7 ~ole/Q, heliu~ at 2 . 37 ~ol~/s, and m~thane at O.39 mmole/s was fed through lin2 8 to the ti~charge operated at 2500 W, and addi-tio~al ;oetha~ fed to the dow~tre~ jet at 0.26 ~ole/s throu~h li~ 9. A substrate tempe~ature o~ about 1100 ~ wa~
ma~a1~d u~i~g additional ~eating of th~ backside wit~ a radiant heater. Operation in thi~ manner for 1 hour produced a dia~o~d fil~ o~ the sub~trat~ as evidenced by a character~
i~tic Ra~an ~atur~ at 1333 cm 1. Th~ ~a88 equivale~t dia-~ond depositio~ rate was 1.7 micron/h oYer a 9 c~ 2 surfacearea of the su~strate.
2~ 3~7 E~.~
An e~periment wa~ performed i~ which a molybdenum substrate was mounted on a water-cooled copper block and positioned 5 cm do~nstream from the no~zle exit a~ in Figure 1. For a period of one hour, 2.9 m~ole/s of heliu~ mixed with 29 ~ole/~ hydrogen wa~ fed through li~e 8 to a Z440 W
di~charge operating at 207 Torr; a~d 0.32 ~olelB of ~ethane was ~ed to the downstr@am jet usin~ line 9. During thiQ
period, a ther~ocouple welded to the front surface of ~the ~ubstrate recorded temperatures below 575 ~ a~ter an initial, brief, ma$i~u~ tempera~ure o~ 583 K. A dia~ond film was deposited i~ the area o~ the ther~ocouple bead aæ evidenced by Ra~an spectra with diamond features at 1333 c~-l a~d having qua].ity ~aotor~, Q ~ 2.5 to 4.2. Beta back~oatteri~g ~ea~urements iQdicated a deposi~io~ rate o~ 0.4 micron/h.
~ 9 Operation oP the apparatus in Figure 1 by ~upplying 23.7 m~ole/s hydrogen and 2.37 m~ole~ heliu~ through line 8 to a Z400 W di~charge at a pres~uce o~ 260 Torr and ~eeding 0.39 m~ole/s methsne to the downsltrea~ jet through line 9 re~ulted in h~ating a~ alu~inu~ nitride ~u~strate, 6 cm ~rom the no2zl~ e~it and at an a~bient pre~sure o~ 17 Torr, to a te~pera~ur~ of 840 ~. A dia~ond ~llm was de~osited at a rate greater tha~ 10 ~icron/h o~hibiti~g charact~ristic Raman dia~o~d ~ak~ ~ar 1338 e~
0~2rat~g th~ apparatus in F:igure 1 i~l the saDIle manner (8alll~ d~cha~ ower and p~e~cur~; ~a~o ga~ flows) as in ~x~pl~ 9, but ~ith a silico~ carblde ~ub~trate positioned 30 6 c~ downs~rea~ o~ the ~ozzle exit resulted in a ~ub~rate te~perature of about 740 g. A diamond $ilm having a charact@riskic Ra~a~ peak with a quality factor Q = 3 was deposited at a peak rate of about 10 micron/h.
.
2~ ~3~7 ~A~ 11 A ~ilicon nitride sub~trate was positioned 6 cm down~tream c~ the nozzle inlet, and 29 mmole/s hydrogen with 2.9 mmole/s helium were fed through lin~ 8 to a 218 Torr, 2700 W discharge, a8 ~hown in Figur2 1. To the jet was fed 0.32 ~mole/~ methane through line 9. The substrate temperature was raiYed to a~out 1125 ~ u8ing 500 W 0~
additional electrical heating, and a~er 12.5 h o~eration in this mode, an adherent diamond ~il~ having an average thickness o~ 10 micron~ and exhibiting a characteri~tic Ra~an diamond pea~ at 1334 cm 1 with a quality factor Q Y 5. The `` adher~nce o~ the fil~ wa~ evidenced by survival o~ a sandbla~t te~t u~ gla~s bead~ and by ~ur~ival o~ the fil~-sub~tra~e i~terface when used i~ a m~chi~ing operation.
! .
Consequ~ntly, under ~ome conditiolls of operation, it may be nece~ary to cool the ~ub~trate, ~o that the ~ub~trate holder may be provided with cooling means, not shown. Ths substrat@ i~ preferably maintained at a temperature between 300 and 1100K. ~nder other conditions of operation, it may be de3ira~1e to 3upply additional heat to the substrate, ~o that the ~ub~trate holder may be proYided with conventional mean~ ~or heating the substrate, not shown.
Pre~erably, the substrate will be oriented sub~tantially perpendicular to the flow o~ the plasma jet. This will tend to maximize the rate o~ deposition of the diamond coating.
However, the substrate holder may be provided with means for pivoting the sub~trate 80 that the area that i8 contacted may be changed from a circle to an oval, thus i~creasing the coating area.
Reference i8 made to ~IGURE 2, which shows an embodiment employing a radio ~requency (r~) electrical di~charge ~o acti-vate the gas, instead o~ the dc discharge de~cribed above.
Power supply 17 of Fig. 1 i~ replalced by a radio ~requency power supply 19 and th~ electrical lead~ 13 and 14 are replaced by el~ctrical leads 20 al~d 21 which may then be coaxial cables to reduce electricall 108~ when higher rf ~requencies ar~ employed. Dischas~g~ cha~ber 3 o~ Fig. 1 i~
replaced by di scharg~ chamber 22 D~ad~ o~ a nonconducting sub#ta~c~ . guar~z or ~YRE~ a~d 18 ~u~rounded by an rf coil 2~. Th~ di~aion~ and nu~r of tus~ in coil 23 con~e~o~ally depend upoa th~ ~reque~cy ~nd impedence requir~ ts of th~ r~ power supply 19. This will be readily deter~in~d by o~e a~illed in ~he a~t. A~ higher powe~ level~
it will be nece~ary to cool coil 23, by pa88ing a cooling ~luid such a~ ~ater through it (not shown in the figure~.
Whe~ a conducting ~luit i~ u~ed it will have to be i~olated from electrical ground, e.g. by passin~ it through a long length of nonconducting tubing 80 that th~ length of 2~3~
conducting liquid used ha3 a high electrical re~ista~ce to ground. The rf power i8 inductively coupled to the gas pa~s-ing through the discharge chamber 22 producing a~ rf electri-cal di~charge lnside chamber 22. This type o~ dischar~e avoids eleetrode~ being in contact with the gas and is thus use~ul when unusually pure dia~ond~ are required, for instance ~or use in semiconductors. All o~her component~ in Figure 2 are the same as those identified in Figure 1.
In another embodiment of the invention, as shown in Figure 3, ~he electrical power that ac~ivates the ga~ i8 furnished by a microwave power supply 24 coupled to the di~-charge chamber 25 th~ou~h an appropriate wave guide 26 and coupling device 27. The dîscharge ~ha~ber 25 also ~erves as a ~icrowave resonant cavity 80 that the hlgh el~ctro~a~ne~ie ~ields created therein ionize the gas ~ed to chamb~r 25 through ~eed line 28 to create a plasma. Also shown i~ ring injector 29, which ~erve8 to direet and concentrate the car-bon-containin8 gab 80 that a high~r proportio~ of the gas contacts the sub~trate. Although not shown in F~gures 1 and 2, a ring injector can be employecl in the apparatus shown in tho~e Figure~ ~o~ the same purpose!. The ri~g injector 29 may also be us~d to in~eet an additiorlal roacta~t gaa downstream o~ th~ noz21~. Thi8 e~bodiment allow8 the sub8trate to be positio~ed furth~ ~ro~ th~ no2~ hi~ retalning the abil-ity to adju~t t~ substrate-to-no2;zle tista~c~ independ~n~ly o~ th~ di~tanc~ between the ~ub~trate and th~ poin~ of do~n-~trea~ ctio~. Thi~ ~leæi~ility allow~ for g~eater con-trol of p~ocosæ p~raMcters leading to optimization of diamond growt~ co~dition~. All other compo~ent8 o~ Figure 3 are the ~a~e as tho8e identified in Figure 1.
Representative ~ubstrate~ include silicon, nickel, gal-liu~ ar~nide, titanium, copper, copper-carbon composite, alu~inu~ ni~ride, ~ilicon carbide, aluminu~-silicon-carbon , .
2~ ~3~
compo~ite, alumina, molybdenum, gold, ~pinel, ?ilica, tung-sten, graphite, copper-tung~1:en alloys and 8 licon-iron.
Surpri~ingly, the proces~ according to the invention results in the produetion of diamond coatings on the sub-5 strate, in~t~ad of any of the many other form~ o~ carbon suchas graphite, amorphoua carbon, hydrogenated carbon, gla88y carbon or oth~r carbon allotropes. Thi3 i8 con~.irmed by Raman ~pec~ro copy, i~ the ~ollowing ~s~ples, with the characteristic dia~ond peak seen a~ about 1332 cm 1, The 19 esact location of the peak i8 determined by a number o~ fac-tors, e.g. ~he strain between the f ilm and the substrate.
The purity o~ the dia~ond deposit i8 indicated by the heigh~
o~ the scatt~red Raman pea~ and the peak width. A diamont quality factor, Q, i8 used herein to refer to the ratio o~
the peak intensity above the underlying continuum to the intensity o~ the u~derlaying co~tinuu~ above the minimum in the baaeline in the range o~ 500 to 1700 c~-l. Thi~
continuum i8 probably aasociated with graphitle, which has a ~catt~ring e~iciency about 100 times that of diamond. Qual-ity ~actorn a~ high as 27 hav~ b~n observed. It i8 to beunders~ood, how~ver, that a~ in natural dia~onds, 3mall a~ount~ o~ i~purities, ~uch a~ hy~drogen, ~it-rogen or silicon may be pre~ent. In ~o~e ~bodiments it ~ay actually be de3irable to lntroduce llimpuritle81', such as when the diamond coating i~ dop~ to for~ p- and ~-type material8.
Th~ apl?~r~tus show in Figur~ 1 was opera~d ~or 6 hour~
at a~ applied voltage o~ 109S voïts and current o~ 2.0 ampe~e~, ~ith a discharge power o:~ 2200 W while ~eeding hydro-30 gen at 23.7 ~ole/s and hellu~ at 2.37 ~ole/s through feedline 8. Methane was a~ded at 0.13 mmole/s in the nozzle through fe~d lin~ 9 and orifice~ 1~. The pre~ure in the plas~a chamber wa~ 127 torr and that in the depo~ition cha~nber was 17 torr. The discharge gas ~emperature wa about 2 ~ -7 ~
; 14--1600~: and the e:i~panded jet temperature was 900~:. A ~ilicon ~ubstrate, 8 cm down~tream o~ the nozzle, wa~ maintained at a temperature o~ 1100Q~ by the addition of 200 watts of electri-cal energy to the ~ubstrate holder 5 . A diamond f ilm h~ving 5 an average thickn@ss o~ 1-2 micron~ was de~o3ited over the entire 16 csll2 expo~ed surface of the sub~trate. A Raman spectrum of the fil~ e~hibitet the diamond feature at 1332 cn~~ on an underlying continuum oi~ comparable magnitude.
~-ray di~fraction analyRis o~ the ~ilm confirmed the presence 10 of crystalline diamond with 30me a-SiC at the interface.
There was no indication of the pre~ence of graphite, yet the Q was only 0.51.
~X~I~ .2 Rytro~e~, helium, and o~cygen, a~ the respec~ive flow 15 rate~ of 23 . 7, 2 . 37, 0 . 024 ~ole/~ were fet to ~he di charge in Figure 1 through ~eed line 8. A silicon sub~trate main-tained at about lOOO-K was positioned at a 30- angle to the jet a~i8 7 c~ ~rom the nozzle. W~th the di6charge opera~ing at 2360 W, 1180 volt~ and 2 amperes, the discharge gas temper-20 ature was 1640 R. Mathane was added at 0 . 39 ~ole/ 8 to thejet through a ring injector locat~d 2 cm down~tream of the nozzla, a~ th~l3 abov~ condition~ for 305 min. A diamont film having a mea~l thic~ over a 6 cla2 area of û.6 ~lcrons wa6 p~oduc~d on the~ ~ubstrate. Th~ a ga~e a ~s~an spec- -25 truls with 1:b~ ond feature ~ear 133~ ~-1 with a quality ~aetor, Q a 22.
E~ ` .
A ~olybd~u~ substrate was ~aai~talned at a t~pera~ure o~ 940-1~ (by h~ati~ el~ctrically) at a di~tance o~ 9 cm 30 rro~ the noz~l~ Or ~h~ apparatu~ ~hown in Figure 1. ~ydrog@n and heliula gas~s were f~d at respec~ive flows of 23 . 7 and 2 . 37 ~ole/~ to th~ discharge through feed liIle 8. While operating the discharge at 2500 W and 228 torr, me~hane was added aLt O . 39 ~mol~/s to the downstreala je~: through ~eed line 9 . This 2 ~ 1 ~ 3 6 7 re~ulted i~ a discharge gas temperature of 2330~K and an expanded jet temperature o~ 1170K~ Operation at these con-dition~ for one ~our r@sulted i~ production of a 16 cm2 diamond film covering the espoged ~urface of the substrate and having a ma~i~u~ thickness of 2-3 microns. A Raman ~pectrum o~ th~ ~ilm exhibited the diamond ~eature at 1334 ~AMPL~ 4 In-a ~imilar experiment to that d~scribed in E~ample 5, a molybdenum ~ubstrate was maintained at a temperature of 1065~. by electrical heating at a di~tance o~ 9 cm from the nozzle of the apparatu~ ~hown in Fig. 1. ~ydrogen and helium gases were ~ed at respective ~lows of 23.7 and 2.37 ~mole/s to the discharg~ through feed line 8. While operating the di3charg~ at 2500 W and 228 torr, a mi~rture of 0 . 77 ~ ole/~
o~ methane and 0.08 m~ole~/s of o~ygen were added to the ~ownstrea~ j~t through feed line 9. Operation st the~e condi-tions for on~ hour resulted in production o~ a 16 cm2 dia-mond film covering the espo3ed ~urface of the subs~rate and having an avera~e fil~ thickness o~ 4-5 ~icrons. A Raman spectrum o~ the ~ e~hib~t~d th~ diamond feature at 1338 c~
In a ~i~ilar ~p~rim~nt tho appa~atus o~ Figure 1 waa u~ed e~cept ~o ~ner~y ~as applied to ~he sub~tra~e holder which was allow~d ~o 8@~ it~ ow~ te~p~ratur~, 815~. Th~
sub~t~at~ ~a~ ~uaxtz ~lseed 7.5 c~ ~ro~ t~e noz~l~ esi~, hydro~e~ a~d h~liu~ were ~ed throu~h the di~charge at 23.7 a~d 2.3~ ~ole/~ respectively, 0.39 m~ole/s o~ ~ethane were injected i~o the nozzle e~i~ section through ~eed line 9, and the discharge was operated at 2l8o watt3 at a total 30 pressure o~ 139 ~orr. Thi~ r~sulted in a discharg~ gas temperature o~ 1600~ and an e~pa~ded jet temperature of 8600g. The pre3sure i~ ~h~ deposi~ion cha~b~r wa~ 17.4 torr. A dia~o~d ~il~ was deposi~ed as i~dicated by the Raman peak with a quality factor o~ 2.8.
2~ ~ ~3~
~ 6 I~ a~oth~r e~periment using the apparatus ~hown in Fig-ure l, a molybdenum ~ubstrate was h@ld 9 cm ~rom the nozzle exit, and wa3 heated only by energy from the do~nstream jet 5 expanding ~ro~ an up~trea~ pres~ure of 224 torr into the depo3ition chamber at a pre~sure of 17 torr. Feeding a mixture o~ hydroge~ at 23.7 mmole/s and heliu~ at 2.37 m~ole/~ throu~h line U to the discharge operat~d at 2050 W, and feeting methane to the downgtream jet at 0.39 mmole/~
through line 9, resulted in a subsgrate temperature of 71SK. Operation in this ~a~ner for 8 hours produced a dia~ond film on the substrate as evidenced by a character-istic Rama~ f@ature at 1333 cm 1 w~th a quality ~actor greater than 1.
~3~PLE_7 In an experi~ent using the app~ratu~ shown in Figure 1, a silicon substrate was held 11 c~ ~rom the nozzle e2it at a 30 degree angle relative to the jet and wa~ heated only by energy ~ro~ ~h~ down~tream jet e3~a~ding ~rom an upstream pressure o~ 140 Torr into the deposition cha~ber at a pre~-sure o~ 18 Torr. A oli~cture o~ hydrogen at 23~7 ~ole/Q, heliu~ at 2 . 37 ~ol~/s, and m~thane at O.39 mmole/s was fed through lin2 8 to the ti~charge operated at 2500 W, and addi-tio~al ;oetha~ fed to the dow~tre~ jet at 0.26 ~ole/s throu~h li~ 9. A substrate tempe~ature o~ about 1100 ~ wa~
ma~a1~d u~i~g additional ~eating of th~ backside wit~ a radiant heater. Operation in thi~ manner for 1 hour produced a dia~o~d fil~ o~ the sub~trat~ as evidenced by a character~
i~tic Ra~an ~atur~ at 1333 cm 1. Th~ ~a88 equivale~t dia-~ond depositio~ rate was 1.7 micron/h oYer a 9 c~ 2 surfacearea of the su~strate.
2~ 3~7 E~.~
An e~periment wa~ performed i~ which a molybdenum substrate was mounted on a water-cooled copper block and positioned 5 cm do~nstream from the no~zle exit a~ in Figure 1. For a period of one hour, 2.9 m~ole/s of heliu~ mixed with 29 ~ole/~ hydrogen wa~ fed through li~e 8 to a Z440 W
di~charge operating at 207 Torr; a~d 0.32 ~olelB of ~ethane was ~ed to the downstr@am jet usin~ line 9. During thiQ
period, a ther~ocouple welded to the front surface of ~the ~ubstrate recorded temperatures below 575 ~ a~ter an initial, brief, ma$i~u~ tempera~ure o~ 583 K. A dia~ond film was deposited i~ the area o~ the ther~ocouple bead aæ evidenced by Ra~an spectra with diamond features at 1333 c~-l a~d having qua].ity ~aotor~, Q ~ 2.5 to 4.2. Beta back~oatteri~g ~ea~urements iQdicated a deposi~io~ rate o~ 0.4 micron/h.
~ 9 Operation oP the apparatus in Figure 1 by ~upplying 23.7 m~ole/s hydrogen and 2.37 m~ole~ heliu~ through line 8 to a Z400 W di~charge at a pres~uce o~ 260 Torr and ~eeding 0.39 m~ole/s methsne to the downsltrea~ jet through line 9 re~ulted in h~ating a~ alu~inu~ nitride ~u~strate, 6 cm ~rom the no2zl~ e~it and at an a~bient pre~sure o~ 17 Torr, to a te~pera~ur~ of 840 ~. A dia~ond ~llm was de~osited at a rate greater tha~ 10 ~icron/h o~hibiti~g charact~ristic Raman dia~o~d ~ak~ ~ar 1338 e~
0~2rat~g th~ apparatus in F:igure 1 i~l the saDIle manner (8alll~ d~cha~ ower and p~e~cur~; ~a~o ga~ flows) as in ~x~pl~ 9, but ~ith a silico~ carblde ~ub~trate positioned 30 6 c~ downs~rea~ o~ the ~ozzle exit resulted in a ~ub~rate te~perature of about 740 g. A diamond $ilm having a charact@riskic Ra~a~ peak with a quality factor Q = 3 was deposited at a peak rate of about 10 micron/h.
.
2~ ~3~7 ~A~ 11 A ~ilicon nitride sub~trate was positioned 6 cm down~tream c~ the nozzle inlet, and 29 mmole/s hydrogen with 2.9 mmole/s helium were fed through lin~ 8 to a 218 Torr, 2700 W discharge, a8 ~hown in Figur2 1. To the jet was fed 0.32 ~mole/~ methane through line 9. The substrate temperature was raiYed to a~out 1125 ~ u8ing 500 W 0~
additional electrical heating, and a~er 12.5 h o~eration in this mode, an adherent diamond ~il~ having an average thickness o~ 10 micron~ and exhibiting a characteri~tic Ra~an diamond pea~ at 1334 cm 1 with a quality factor Q Y 5. The `` adher~nce o~ the fil~ wa~ evidenced by survival o~ a sandbla~t te~t u~ gla~s bead~ and by ~ur~ival o~ the fil~-sub~tra~e i~terface when used i~ a m~chi~ing operation.
! .
Claims (12)
1. A process for forming diamond coatings in which a plasma-producing gas of mixture of gases is passed through a low temperature silent discharge to generate a low temperature non-equilibrium plasma gas stream, the plasma gas stream is adiabatically expanded into a region of lower pressure to form a plasma gas stream of highly ionized and dissociated gases that is then directed onto the surface of a substrate, characterized in that a carbon-containing gas is injected into the plasma gas stream during or after the expansion into
2. A process for forming diamond coatings as claimed in claim 1, further characterized in that the temperature of the plasma gas stream is 250 to 1400°K.
3. A process for forming diamond coatings as claimed in claim 1 or 2, further characterized in that neither the carbon-containing gas nor the products that are formed when it reacts with the activated hydrogen are exposed to the discharge.
4. A process for forming diamond coatings as claimed in claim 1,2 or 3, further characterized in that the plasma gas stream is passed through a nozzle from which it expands into an expansion chamber forming the region of lower pressure
5. A process for forming diamond coatings as claimed in claim 4, further characterized in that the substrate is located in the expansion chamber from about 6 to 10 cm from the nozzle.
6. A process for forming diamond coatings as claimed in claim 4, further characterized in that the carbon containing gas is introduced into the nozzle downstream of its smallest diameter .
7. A process for forming diamond coatings as claimed in any of the preceding claims, further characterized in that the plasma-producing gas is hydrogen or a mixture of hydrogen and an inert gas.
8. A process for forming diamond coatings as claimed in any of the preceding claims, further characterized in that the carbon-containing gas is a hydrocarbon containing one to four carbon atoms.
9. A process for forming diamond coatings as claimed in any of the preceding claims, further characterized in that the hydrocarbon is methane.
10. A process or forming diamond coatings as claimed in any of the preceding claims, further characterized in that the carbon-containing gas is ethanol, acetone, or carbon monoxide.
11. A process for forming diamond coatings as claimed in any of the preceding claims, further characterized in that the temperature of the plasma gas stream prior to expansion is in the range from about 500 to about2000°K..
12. A process for forming diamond coatings as claimed in any of the preceding claims, further characterized in that the temperature of the plasma gas stream prior to expansion is in the range from about 1300 to about 1800°K.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US340,995 | 1989-04-20 | ||
| US07/340,995 US5104634A (en) | 1989-04-20 | 1989-04-20 | Process for forming diamond coating using a silent discharge plasma jet process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2014367A1 true CA2014367A1 (en) | 1990-10-20 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002014367A Abandoned CA2014367A1 (en) | 1989-04-20 | 1990-04-11 | Process for forming diamond coating using a silent discharge plasma jet process |
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| Country | Link |
|---|---|
| US (1) | US5104634A (en) |
| EP (1) | EP0394735A3 (en) |
| JP (1) | JPH02296796A (en) |
| CA (1) | CA2014367A1 (en) |
| IL (1) | IL94108A (en) |
| ZA (1) | ZA903022B (en) |
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| US5256205A (en) * | 1990-05-09 | 1993-10-26 | Jet Process Corporation | Microwave plasma assisted supersonic gas jet deposition of thin film materials |
| US5356672A (en) * | 1990-05-09 | 1994-10-18 | Jet Process Corporation | Method for microwave plasma assisted supersonic gas jet deposition of thin films |
| EP0491521B1 (en) * | 1990-12-15 | 1997-03-12 | Fujitsu Limited | Process for producing diamond film |
| US5204144A (en) * | 1991-05-10 | 1993-04-20 | Celestech, Inc. | Method for plasma deposition on apertured substrates |
| US5411758A (en) * | 1991-10-09 | 1995-05-02 | Norton Company | Method of making synthetic diamond wear component |
| US5286331A (en) * | 1991-11-01 | 1994-02-15 | International Business Machines Corporation | Supersonic molecular beam etching of surfaces |
| DE4204650C1 (en) * | 1992-02-15 | 1993-07-08 | Hoffmeister, Helmut, Dr., 4400 Muenster, De | |
| US5358596A (en) * | 1992-07-02 | 1994-10-25 | The Board Of Trustees Of The Leland Stanford Junior University | Method and apparatus for growing diamond films |
| CA2112308C (en) * | 1993-01-22 | 2000-08-15 | Louis K. Bigelow | Method of making white diamond film |
| JPH0794303A (en) * | 1993-05-04 | 1995-04-07 | Kobe Steel Ltd | Highly oriented diamond thin- film thermistor |
| US5442199A (en) * | 1993-05-14 | 1995-08-15 | Kobe Steel Usa, Inc. | Diamond hetero-junction rectifying element |
| US5560779A (en) * | 1993-07-12 | 1996-10-01 | Olin Corporation | Apparatus for synthesizing diamond films utilizing an arc plasma |
| US5560897A (en) * | 1993-10-07 | 1996-10-01 | The Regents Of The University Of California Office Of Technology Transfer | Plasma-assisted conversion of solid hydrocarbon to diamond |
| US5578901A (en) * | 1994-02-14 | 1996-11-26 | E. I. Du Pont De Nemours And Company | Diamond fiber field emitters |
| CA2185217A1 (en) * | 1994-04-06 | 1995-10-19 | Rointan F. Bunshah | Process to produce diamond films |
| US5637950A (en) * | 1994-10-31 | 1997-06-10 | Lucent Technologies Inc. | Field emission devices employing enhanced diamond field emitters |
| US5551983A (en) * | 1994-11-01 | 1996-09-03 | Celestech, Inc. | Method and apparatus for depositing a substance with temperature control |
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| JPS63282200A (en) * | 1987-05-14 | 1988-11-18 | Fujitsu Ltd | Method of chemical vapor growth for diamond |
| US4822466A (en) * | 1987-06-25 | 1989-04-18 | University Of Houston - University Park | Chemically bonded diamond films and method for producing same |
-
1989
- 1989-04-20 US US07/340,995 patent/US5104634A/en not_active Expired - Fee Related
-
1990
- 1990-04-09 EP EP19900106785 patent/EP0394735A3/en not_active Withdrawn
- 1990-04-11 CA CA002014367A patent/CA2014367A1/en not_active Abandoned
- 1990-04-18 IL IL9410890A patent/IL94108A/en not_active IP Right Cessation
- 1990-04-20 ZA ZA903022A patent/ZA903022B/en unknown
- 1990-04-20 JP JP2105148A patent/JPH02296796A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| IL94108A (en) | 1994-11-11 |
| ZA903022B (en) | 1990-12-28 |
| EP0394735A2 (en) | 1990-10-31 |
| EP0394735A3 (en) | 1991-01-23 |
| US5104634A (en) | 1992-04-14 |
| IL94108A0 (en) | 1991-01-31 |
| JPH02296796A (en) | 1990-12-07 |
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